Method and apparatus providing combined spacer and optical lens element

ABSTRACT

A method and apparatus used for forming a lens and spacer combination, and imager module employing the spacer and lens combination. The apparatus includes a mold having a base, spacer section, and mold feature. The method includes using the mold with a blank to create a spacer that includes an integral lens. The spacer and lens combination and imager modules can be formed on a wafer level.

FIELD OF THE INVENTION

The embodiments described herein relate to spacers and optical lenseswhich may be used in imaging devices, and methods of their manufacture.

BACKGROUND OF THE INVENTION

Microelectronic imagers are used in a multitude of electronic devices.As microelectronic imagers have decreased in size and improvements havebeen made with respect to image quality and resolution, they have becomecommonplace devices and are used, for example, in computers, mobiletelephones, and personal digital assistants (PDAs), in addition to theirtraditional uses in digital cameras.

Microelectronic imagers include image sensors that typically use chargedcoupled device (CCD) systems and complementary metal-oxide semiconductor(CMOS) systems, as well as other solid state imager systems.

Microelectronic imager modules, such as module 150 shown in FIG. 1, areoften fabricated at a wafer level in which many such modules are formedas part of a wafer assembly and then separated. The imager module 150includes an imager die 108, which includes an imager pixel array 106 andassociated circuits (not shown). Imager pixel array 106 may be a CCD orCMOS imager pixel array, or any other type of solid state imager pixelarray. Imager module 150 may also include a lens structure 112, having aspacer 109 and at least one lens element 111 arranged on a portion of alens wafer 510. Spacer 109 maintains lens element 111 at a properdistance from imager pixel array 106, such that light striking lenselement 111 is directed appropriately to imager pixel array 106. Spacer109 may be bonded to imager die 108 by a bonding material 104 such asepoxy. Typically, lens element 111 comprises one or more opticallytransmissive lenses made of glass or plastic material configured tofocus light radiation onto imager pixel array 106. In addition, the lensstructure 112 may be combined with another optically transmissiveelement, such as a package lid.

In practice, imager modules 150 are fabricated at a wafer level in massrather than individually. As shown in a top-down view in FIG. 2A and across-sectional view in FIG. 2B—both FIGS. showing a portion of a largerwafer assembly—multiple imager dies 108 a-108 d (four shown here forsimplified illustration) are fabricated on a semiconductor wafer 90.Each die includes a respective imager pixel array (FIG. 2B illustratestwo arrays 106 a, 106 b because it is a cross-sectional view). As shownin FIGS. 3A and 3B, multiple lens elements 111 a-111 d (again, fourshown here for simplified illustration), corresponding in number andlocation to the imager pixel arrays 106 on imager wafer 90 (FIGS. 2A and2B), may be fabricated on a lens wafer 510. A replication process, forexample an ultraviolet embossing, can be used to duplicate the surfacetopology of a lens master onto a thin film of an ultraviolet-curableepoxy resin applied to lens wafer 510. As shown in FIG. 4A, lens wafer510 is placed so that it is separated from imager wafer 90 by spacers109, the latter typically formed on a separate spacer wafer.Additionally, lens wafer 510 is located such that lens elements 111a-111 d (FIG. 4A illustrates only 111 a and 111 b because it is across-sectional view) are optically aligned with imager dies 108 a-108 d(FIG. 4A illustrates only 108 a and 108 b because it is across-sectional view) to form a plurality of imager modules 150 a, 150 b(other imager modules are formed, but not shown in FIG. 4A). As shown inFIG. 4C, the imager modules 150 a, 150 b may then be separated intoindividual imager modules 150 a, 150 b by dicing.

One technique for creating the spacers 109 is to place a mask over aglass or polymer wafer material used for spacer 109 prior to usingfine-grit sand to blast through these non-masked portions of the glassor polymer wafer. This creates a through-hole spacer 109. Anothertechnique for creating a through-hole spacer 109 is to place an etchstop material over a glass or polymer wafer and apply an etchingmaterial that removes the glass or polymer in those portions where theetch stop material is not present. Both of these techniques haveshortfalls. Primarily, both techniques can result in a through-hole thathas at least some taper resulting from a greater application of eitherfine-grit sand or etching material to the portion of the hole closest towhere the removal media is being applied. This taper can appear wherenon-tapered through-holes are required, or can more greatly exaggerate adesired taper. Accordingly, a method of fabrication of spacers 109 isrequired where the dimensions of the spacer can be more preciselymaintained.

In addition to fabrication problems, the fabrication of spacers 109 on aseparate wafer introduces additional steps into the imager assemblyprocess. Currently when assembling an imager, the spacer 109 wafer mustbe aligned over the imager wafer 90, and the lens wafer 510 must then bealigned over the spacer 109 wafer. This creates multiple opportunitiesfor misalignment.

Referring now to FIG. 4B, in cases where multiple lenses (stacked overone another) are required, an additional spacer 109 a wafer must beplaced over lens wafer 510, and an additional lens wafer 510 a with lenselements 111 e-111 f must be placed over the additional level of spacers109 a. With each additional lens element that must be added to theimager module fabrication becomes even more complex, and the likelihoodof misalignment further increases.

Accordingly, there is a need for an apparatus and method that providesthrough holes that have reduced inadvertent tapering during formation ofthe spacers, reduces the assembly steps necessary for both single- andmulti-lens imagers, and reduces the likelihood of misalignment for bothsingle- and multi-lens imagers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an imager module.

FIGS. 2A-2B illustrate a portion of an imager wafer assembly.

FIGS. 3A-3B illustrate a portion of a lens wafer assembly.

FIG. 4A illustrates a portion of an imager module assembly with a singlelens element over each imager array.

FIG. 4B illustrates a portion of an imager module assembly with two lenselements over each imager array.

FIG. 4C illustrates a portion of an imager module assembly with a singlelens element over each imager array, and shows where imager modules areseparated by dicing.

FIG. 5A illustrates a cross-sectional view of a convex form mold forproducing a combination spacer lens wafer having a concave lensaccording to a first example embodiment described herein.

FIG. 5B illustrates a cross-sectional view of a concave form mold forproducing a combination spacer lens wafer having a convex lens accordingto a second example embodiment described herein.

FIG. 6A illustrates an overhead view of a convex form mold for producinga combination spacer lens wafer having a concave lens according to afirst example embodiment described herein.

FIG. 6B illustrates an overhead view of a concave form mold forproducing a combination spacer lens wafer having a convex lens accordingto a second example embodiment described herein.

FIGS. 7A, 8A, and 9A illustrate steps of a method of making acombination spacer lens wafer having a concave lens according to a firstexample embodiment described herein.

FIGS. 7B, 8B, and 9B illustrate steps of a method of making acombination spacer lens wafer having a convex lens according to a secondexample embodiment described herein.

FIG. 10A illustrates an unfinished combination spacer lens wafer havinga concave lens according to a first example embodiment described herein.

FIG. 10B illustrates an unfinished combination spacer lens wafer havinga convex lens according to a second example embodiment described herein.

FIG. 11A illustrates a finished combination spacer lens wafer having aconcave lens according to a first example embodiment described herein.

FIG. 11B illustrates a finished combination spacer lens wafer having aconvex lens according to a second example embodiment described herein.

FIG. 12A illustrates a cross-sectional view of an assembled imagermodule having a single concave combination spacer lens wafer accordingto a first example embodiment described herein.

FIG. 12B illustrates a cross-sectional view of an assembled imagermodule having a single convex combination spacer lens wafer according toa second example embodiment described herein.

FIG. 12C illustrates a cross-sectional view of an assembled imagermodule having a single concave combination spacer lens wafer, with ablack coating, according to a first example embodiment described herein.

FIG. 12D illustrates a cross-sectional view of an assembled imagermodule having a single convex combination spacer lens wafer, with ablack coating, according to a second example embodiment describedherein.

FIG. 12E illustrates a cross-sectional view of an assembled imagermodule having a single concave combination spacer lens wafer, with ananti-reflective coating, according to a first example embodimentdescribed herein.

FIG. 12F illustrates a cross-sectional view of an assembled imagermodule having a single convex combination spacer lens wafer, with ananti-reflective coating, according to a second example embodimentdescribed herein.

FIG. 13A illustrates a cross-sectional view of a combination spacer lenswafer having a concave lens according to a first example embodimentdescribed herein with lens replication completed.

FIG. 13B illustrates a cross-sectional view of a combination spacer lenswafer having a convex lens according to second example embodimentdescribed herein with lens replication completed.

FIGS. 14A illustrates a cross-sectional view of a combination spacerlens wafer having a concave lens according to a first example embodimentdescribed herein with lens replication and a second combination spacerlens wafer with lens replication.

FIG. 14B illustrates a cross-sectional view of a combination spacer lenswafer having a convex lens according to a second example embodimentdescribed herein with lens replication and a second combination spacerlens wafer with lens replication.

FIG. 15 illustrates a block diagram of a CMOS imaging device constructedusing combination spacer lenses made using methods and apparatuses inaccordance with an example embodiment described herein.

FIG. 16 depicts a system using combination spacer lenses made withmethods and apparatuses in accordance with an example embodimentdescribed herein.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, reference is made to the accompanyingdrawings which form a part hereof, and in which are shown by way ofillustrations specific embodiments that may be practiced. It should beunderstood that like reference numerals represent like elementsthroughout the drawings. These example embodiments are described insufficient detail to enable those skilled in the art to practice them.It is to be understood that other embodiments may be utilized, and thatstructural, material and electrical changes may be made, only some ofwhich are discussed in detail below.

Referring now to FIGS. 12A and 12B, which illustrate two exampleembodiments, embodiments described herein relate to an apparatus andmethod for making combination spacer lens wafers 480 (FIG. 12A) and 485(FIG. 12B). Embodiments described herein also relate to the concavecombination spacer lens wafer 480 (first embodiment) and the convexcombination spacer lens wafer 485 (second embodiment), themselves.

Two embodiments of an apparatus used with a method for makingcombination spacer lens wafers 480 (FIG. 12A) and 485 (FIG. 12B) aredescribed. Convex form mold 200 (FIG. 5A) (first embodiment) is used tomake concave combination spacer lens wafers 480 (first embodiment).Concave form mold 205 (FIG. 5B) (second embodiment) is used to makeconvex combination spacer lens wafer 485 (second embodiment).

Two embodiments of a method for making the combination spacer lenswafers 480 (FIG. 12A) and 485 (FIG. 12B) are also described. These twoembodiments are identical, except that the method (shown in FIGS. 7A,8A, and 9A) (first embodiment) for making a concave combination spacerlens wafer 480 (first embodiment) uses convex form mold 200 (FIG. 5A)(first embodiment) while the method (shown in FIGS. 7B, 8B, and 9B)(second embodiment) for making convex combination spacer lens wafer 485(second embodiment) uses concave form mold 205 (FIG. 5B) (secondembodiment).

The convex form mold 200 (FIG. 5A), the method of making a concavecombination spacer lens wafer 480, and the finished concave combinationspacer lens wafer 480 are described first.

Referring to FIG. 5A, the convex form mold 200—the apparatus for makingconcave combination spacer lens wafer 480 (FIG. 12A)—is now described.Convex form mold 200 has spacer section 401, base 403 and convex moldfeature 420 at the distal end of the spacer section 401. The convex moldfeature 420, however, is not intended to be limiting. A protrusion (moldfeature 420) of any shape can be made to create a correspondingcombination lens portion 490 (FIG. 12A). As such, highly aspherical lensstructures are also possible.

Just as the example embodiment for convex mold feature 420 is notintended to be limiting, the example embodiment for spacer section 401is also not intended to be limiting. Referring now to FIG. 6A (overheadview of FIG. 5A), spacer section 401 is shown having a large square base422, while mold feature 420 which is at the distal end of spacer section401 is shown having a small square base 424. In this embodiment, spacersection 401 tapers between large square base 422 and the small squarebase 424. Spacer section 401, however, can have any shape base 422.Similarly, mold feature 420 can have any shape base 424. As such, spacersection 401 can have any shape, to include a non-tapered shape, or anon-uniform shape. The spacer section 401 and mold feature 420 arepreferably integrally formed.

Referring now to FIGS. 5A and 6A, the convex form mold 200 may also haveoptional alignment elements 240 a, 240 b that can be used to createcorresponding alignment detents 243 a, 243 b (FIG. 8A). These alignmentdetents 243 a, 243 b (FIG. 8A) may be used to align concave combinationspacer lens wafer 480 (FIG. 12A) with imager die 108 (FIG. 12A), oralternatively with another concave combination spacer lens wafer 480(FIG. 12A), a conventional spacer 109 (FIG. 1), or any imager modulepart having appropriate alignment detents 243 a, 243 b (FIG. 8A)complementary to alignment elements 240 a, 240 b. Two symmetricalignment elements 240 a, 240 b are shown, but a single non-symmetricalignment element may also be used in conjunction with a matchingalignment detent in embodiments where fewer alignment elements aredesired.

The method for forming an unfinished concave combination spacer lenswafer 478 (FIG. 10A) is now described with reference to FIGS. 7A, 8A,9A, and 10A. To form an unfinished concave combination spacer lens wafer478, a convex form mold 200 (FIG. 5A) is used.

Referring to FIG. 7A, convex form mold 200 is placed underneath waferblank 210. In one embodiment, wafer blank 210 comprises a float glass.Although glass is described, an optical polymer may also be used. Oneexample of a float glass that may be used is a boro-float glass with acoefficient of thermal expansion between 2 and 5, such as Borofloat® 33from Schott North America, Inc. Whether using glass or an opticalpolymer, the wafer blank 210 may also be in liquid form.

In cases where wafer blank 210 is not in liquid form, wafer blank 210 ismade sufficiently malleable to assume the form of convex form mold200—whether glass or polymer—by heating wafer blank 210 using anysuitable method. Once an appropriate temperature is reached if heatingis being applied, wafer blank 210 is lowered into contact with andpressed on to convex form mold 200. Wafer blank 210 may be heated to anappropriate temperature while on convex form mold 200 to allow convexform mold 200 to penetrate wafer blank 210. Wafer blank 210 may receiveconvex mold feature 420 (FIG. 5A) and spacer section 401 (FIG. 5A) ofconvex form mold 200. Wafer blank 210 may also receive alignmentelements 240 a, 240 b if present.

Referring now to FIG. 8A, once wafer blank 210 has been displaced suchthat spacer section 401 (FIG. 5A), convex mold feature 420 (FIG. 5A),and alignment elements 240 a, 240 b (FIG. 7A) (if present) have beentransferred, wafer blank 210 is allowed to cool so that it will hold itsshape upon removal from convex form mold 200. Depending on the glass orpolymer used for wafer blank 210, an appropriate curing time should beallowed to pass. Also based on the material used for wafer blank 210,the curing can be either an accelerated cooling, a gradual cooling, oralternating heating and cooling to ensure certain properties aredeveloped within the glass or polymer used for wafer blank 210.

Referring now to FIG. 9A, once the appropriate curing or cooling hasoccurred, wafer blank 210 (FIG. 7A) has assumed the shape of convex formmold 200. Once this has occurred, unfinished concave combination spacerlens wafer 478 can be removed from convex form mold 200. Referring nowto FIG. 10A, unfinished concave combination spacer lens wafer 478 has acombination lens portion 490 and a combination spacer portion 495. Theunfinished concave combination spacer lens wafer 478 may also havealignment detents 243 a, 243 b in cases where the form mold 200 (FIG.9A) had corresponding alignment elements 240 a, 240 b (FIG. 9A).

To ensure stability during placement and removal during the fabricationstages, wafer blank 210 (FIG. 7A) in most embodiments will have athickness greater than that desired for use with the imager module 150(FIG. 12A). This additional thickness may require the topmost portion497 of unfinished concave combination spacer lens wafer 478 to undergoadditional finishing through the removal of area 520. Additionalfinishing, however, may not be required for embodiments in which waferblank 210 (FIG. 7A) does not require additional material for addedstability during placement and removal of wafer blank 210 (FIG. 7A)during the fabrication stages.

Even in situations where additional material is unnecessary forstability purposes, grinding and polishing may still be necessary toachieve a flat surface. In these cases, displacement of wafer blank 210(FIG. 7A) results in deformations at topmost portion 497 of unfinishedconcave combination spacer lens wafer 478. Grinding and polishing isperformed to remove these deformations.

Referring now to FIG. 11A, in embodiments where additional finishing isrequired, unfinished concave combination spacer lens wafer 478 (FIG.10A) will undergo a finishing step, which may include grinding, orchemical etching to narrow the distance between the top-most portion 497(FIG. 10A) of unfinished concave combination spacer lens wafer 478 (FIG.10A) and the bottom-most portion 499 (FIG. 10A) of unfinished concavecombination spacer lens wafer 478 (FIG. 10A). The top-most portion 497(FIG. 10A) undergoes the finishing step by removal of area 520. Oncethis thinning has occurred, the result is a finished concave combinationspacer lens wafer 480.

The finished concave combination spacer lens wafer 480 is now describedwith reference to FIG. 12A. Finished concave combination spacer lenswafer 480 has a combination lens portion 490 and a combination spacerportion 495. The combination lens portion 490 acts as the lens, whilethe combination spacer portion 495 acts as a spacer for separating thecombination lens portion 490 a specific distance from the imager pixelarray 106. Finished concave combination spacer lens wafers 480 may alsohave alignment detents 243 a, 243 b (FIG. 11A) in cases where the formmold 200 (FIG. 5A) had corresponding alignment elements 240 a, 240 b(FIG. 5A).

Placing the finished concave combination spacer lens wafer 480 onto awafer containing an imager pixel array 106 fully encloses combinationspacer lens cavity 107. Whatever shape spacer section 401 (FIG. 5A) hasduring formation is the shape that spacer lens cavity 107 will haveafter assembly.

In one embodiment finished concave combination spacer lens wafers 480can be divided into single finished concave combination spacer lenswafers 480. This enables a single finished concave combination spacerlens 480 to be individually placed on an imager pixel array 106.Alternatively, multiple finished concave combination spacer lenses 480can remain joined and be simultaneously placed over and aligned with awafer containing an imager pixel array 106. In this case, alignment canbe done using alignment elements 240 a, 240 b (if present) inconjunction with alignment detents 243 a, 243 b (FIG. 11A).Additionally, moving finished concave combination spacer lens wafers 480can be performed using a vacuum tool, as there are no through-holes inthis combination spacer lens wafer 480 that were present in the priorart.

In cases where additional lenses (in a vertical stack) are required, thefinished concave combination spacer lens wafer 480 can undergoadditional processing steps. Referring now to FIG. 13A, a polymer lensreplication step can be performed on the surface of finished concavecombination spacer lens wafer 480 in order to form a finished concavecombination spacer lens wafer with top-surface mounted polymer lens 600.

In embodiments having additional lenses, achromatization may be achievedby using distinct materials having different optical dispersions(variation of refractive index with wavelength, represented by an Abbenumber). Using two separate materials, one with high dispersion (lowAbbe number, less than or equal to 50), and one with low dispersion(high Abbe number, greater than 50), may avoid chromatic aberrations.Generally, a glass with high dispersion is used for the finished concavecombination spacer lens wafer 480 and an ultraviolet-curable polymer(for example Ormocomp of the ORMOCER® material family from Micro ResistTechnology) with a low dispersion may be used for the top-surfacemounted polymer lens 515. In some cases, however, two different types ofpolymer having different optical dispersions may be used for both thefinished concave combination spacer lens wafer 480 and the top-surfacemounted polymer lens 515.

Referring now to FIG. 14A, finished concave combination spacer lenswafers with top-surface mounted polymer lenses 600 can be stacked toprovide four lenses. While two finished concave combination spacer lenswafers with convex top-surface mounted polymer lenses 600 are shown, oneof the combination spacer lens wafers could be convex, and thetop-surface mounted polymer lenses 515 could be concave. Additionally,any combination of either unfinished 478, 483 (FIGS. 10A, 10B) orfinished combination spacer lens wafers 480, 485 (FIGS. 11A, 11B) can beformed. As such, the number and type of lenses (both top-surface mountedand combination spacer lens wafers) can be tailored to the specificimager's application, while retaining the benefits of simpler assembly,reduced alignment issues, and the prevention of inadvertent tapering ofthrough-holes.

Referring now to FIGS. 12C and 12E, once the finished concavecombination spacer lens wafer 480 (FIG. 11A), or the finished concavecombination spacer lens wafer with top-surface mounted polymer lens 600(FIG. 13A) is completed, additional processing steps can be performed toimprove the performance of the combination spacer lens. For example, ablack coating 612 may be applied on the inside side-walls enclosing thecombination spacer lens cavity 107 to reduce spurious reflections. Sucha coating would improve the signal-to-noise ratio of the imager module150. Alternatively, an anti-reflective coating 617 may be applied on theinside side-walls and lens enclosing the combination spacer lens cavity107 to reduce spurious reflections and increase the transmission of thelens interface. Another alternative is to form an opaque material (i.e.,black polymer or metal) on top-most portion 497 (FIG. 10A) after it hasundergone any necessary finishing step, and prior to application oftop-surface mounted polymer lenses 515 (FIG. 13A). The opaque materialon top-most portion 497 (FIG. 10A) is formed to have an aperture thatallows light to pass through the lens portion of the combination spacerlens wafer 480 (FIG. 11A).

The concave form mold 205 (FIG. 5B), the method of making a finishedconvex combination spacer lens wafer 485 (FIG. 12B), and the finishedconvex combination spacer lens wafer 485 (FIG. 12B) are described next.

Referring now to FIG. 5B, the concave form mold 205—the apparatus formaking convex combination spacer lens wafers 485 (FIG. 12B)—is nowdescribed. Concave form mold 205 has spacer section 401, base 403, andconcave mold feature 425. In this embodiment, the concave mold featuredoes not extend away from the spacer section 401 (as it does in FIG.5A). Instead, mold feature 425 extends into spacer section 401. This isillustrated by the dotted line shown below small square base 424. Theconcave mold feature 425, however, is not intended to be limiting. Acavity (mold feature 425) of any shape can be made to create acorresponding combination lens portion 490 (FIG. 12B). Highly asphericallens structures are also possible.

Just as the example embodiment for convex mold feature 425 is notintended to be limiting, the example embodiment for spacer section 401is also not intended to be limiting. Referring now to FIG. 6B (overheadview of FIG. 5B), spacer section 401 is shown having a large square base422, and a small square base 424 at its top. Unlike the convex form mold200 (FIG. 5A), however, the convex mold feature 425 extends in to spacersection 401 instead of extending away from spacer section 401. Despitethese differences, spacer section 401 can still have any shape base 422.Similarly, mold feature 425 can still have any shape base 424. As such,spacer section 401 can have any shape, to include a non-tapered shape,or a non-uniform shape. The spacer section 401 and mold feature 425 arepreferably integrally formed.

Referring now to FIGS. 5B and 6B, the concave form mold 205 may alsohave optional alignment elements 240 a, 240 b that can be used to createcorresponding alignment detents 243 a, 243 b (FIG. 8B). These alignmentdetents 243 a, 243 b (FIG. 8B) may be used to align convex combinationspacer lens wafer 485 (FIG. 12B) with imager die 108 (FIG. 12B), oralternatively with another convex combination spacer lens wafer 485(FIG. 12B), a conventional spacer 109 (FIG. 1), or any other imagermodule 150 part having appropriate alignment detents 243 a, 243 b (FIG.8B) complementary to alignment elements 240 a, 240 b. Two symmetricalignment elements 240 a, 240 b are shown, but a single non-symmetricalignment element may also be used in conjunction with a matchingalignment detent in embodiments where fewer alignment elements aredesired.

The method for forming an unfinished convex combination spacer lenswafer 483 (FIG. 10B) is now described with reference to FIGS. 7B, 8B,9B, and 10B. To form an unfinished convex combination spacer lens wafer483, a concave form mold 205 (FIG. 5B) is used.

Referring to FIG. 7B, a concave form mold 205 is placed underneath waferblank 210. In one embodiment, wafer blank 210 comprises a float glass.Although glass is described, an optical polymer may also be used. Oneexample of a float glass that may be used is a boro-float glass with acoefficient of thermal expansion between 2 and 5, such as Borofloat® 33from Schott North America, Inc.

To make wafer blank 210 sufficiently malleable to assume the form ofconcave form mold 205—whether glass or polymer—wafer blank 210 may beheated by any suitable method. Once an appropriate temperature isreached if heating is being applied, wafer blank 210 is lowered intocontact with and pressed on to concave form mold 205. Wafer blank 210may be heated to an appropriate temperature while on concave form mold205 to allow concave form mold 205 to penetrate wafer blank 210. Waferblank 210 may receive concave mold feature 425 (FIG. 5B) and spacersection 401 (FIG. 5B) of concave form mold 205. Wafer blank 210 may alsoreceive the alignment elements 240 a, 240 b, if present.

Referring now to FIG. 8B, once wafer blank 210 has been displaced suchthat spacer section 401 (FIG. 5B), concave mold feature 425 (FIG. 5B),and alignment elements 240 a, 240 b (FIG. 5B) (if present) have beentransferred, wafer blank 210 is allowed to cool so that it will hold itsshape upon removal from concave form mold 205. Depending on the glass orpolymer used for wafer blank 210, an appropriate curing time should beallowed to pass. Also based on the material used for wafer blank 210,the curing can be either an accelerated cooling, a gradual cooling, oralternating heating and cooling to ensure certain properties aredeveloped within the glass or polymer used for the wafer blank 210.

Referring now to FIG. 9B, once the appropriate curing or cooling hasoccurred, wafer blank 210 (FIG. 7B) has assumed the shape of concaveform mold 205. Once this has occurred, unfinished convex combinationspacer lens wafer 483 can be removed from mold 205. Referring now toFIG. 10B, unfinished convex combination spacer lens wafer 483 has acombination lens portion 490 and a combination spacer portion 495. Theunfinished convex combination spacer lens wafer 483 may also havealignment detents 243 a, 243 b in cases where the form mold 205 hadcorresponding alignment elements 240 a, 240 b.

To ensure stability during placement and removal during the fabricationstages, wafer blank 210 (FIG. 7B) in most embodiments will have athickness greater than that desired for use with the imager module 150(FIG. 12A). This additional thickness may require the topmost portion497 of the unfinished convex combination spacer lens wafer 483 toundergo additional finishing through the removal of area 525. Additionalfinishing, however, may not be required for embodiments in which waferblank 210 (FIG. 7B) does not require additional material for addedstability during placement and removal of wafer blank 210 (FIG. 7B)during the fabrication stages.

Even in situations where additional material is unnecessary forstability purposes, grinding and polishing may still be necessary toachieve a flat surface. In these cases, displacement of wafer blank 210(FIG. 7B) results in deformations at topmost portion 497 of unfinishedconcave combination spacer lens wafer 483. Grinding and polishing isperformed to remove these deformations.

Referring now to FIG. 11B, in embodiments where additional finishing isrequired, the unfinished convex combination spacer lens wafer 483 willundergo a finishing step, which may include grinding, or chemicaletching to narrow the distance between the top-most portion 497 (FIG.10B) of unfinished convex combination spacer lens wafer 483 (FIG. 10B)and the bottom-most portion 499 (FIG. 10B) of unfinished convexcombination spacer lens wafer 483 (FIG. 10B). The top-most portion 497(FIG. 10B) undergoes the finishing step by removal of area 525. Oncethis thinning has occurred, the result is a finished convex combinationspacer lens wafer 485.

The finished convex combination spacer lens wafer 485 is now describedwith reference to FIG. 12B. Finished convex combination spacer lenswafer 485 has a combination lens portion 490 and a combination spacerportion 495. The combination lens portion 490 acts as the lens, whilethe combination spacer portion 495 acts as a spacer for separating thecombination lens portion 490 a specific distance from the imager pixelarray 106. Finished convex combination spacer lens wafers 485 may alsohave alignment detents 243 a, 243 b (FIG. 11B) in cases where the formmold 205 (FIG. 5B) had corresponding alignment elements 240 a, 240 b(FIG. 5B).

Placing the finished convex combination spacer lens wafer 485 onto awafer containing an imager pixel array 106 fully encloses combinationspacer lens cavity 107. Whatever shape spacer section 401 (FIG. 5B) hasduring formation is the shape that spacer lens cavity 107 will haveafter assembly.

In one embodiment finished convex combination spacer lens wafers 485 canbe divided into single finished convex combination spacer lens wafers485. This enables a single finished convex combination spacer lens 485to be individually placed on an imager pixel array 106. Alternatively,multiple finished convex combination spacer lenses 485 can remain joinedand be simultaneously placed over and aligned with an imager pixel array106. In this case, alignment can be done using alignment elements 240 a,240 b (FIG. 9B) (if present) in conjunction with alignment detents 243a, 243 b (FIG. 9B). Additionally, moving finished convex combinationspacer lens wafers 485 can be performed using a vacuum tool, as thereare no through-holes in this combination spacer lens wafer 485 that werepresent in the prior art.

In cases where additional lenses (in a vertical stack) are required, thefinished convex combination spacer lens wafer 485 can undergo additionalprocessing steps. Referring now to FIG. 13B, a polymer lens replicationstep can be performed on the surface of finished convex combinationspacer lens wafer 485 in order to form a finished convex combinationspacer lens wafer with top-surface mounted polymer lens 605.

In embodiments having additional lenses, achromatization may be achievedby using distinct materials having different optical dispersions(variation of refractive index with wavelength, represented by an Abbenumber). Using two separate materials, one with high dispersion (lowAbbe number, less than or equal to 50), and one with low dispersion(high Abbe number, greater than 50), may avoid chromatic aberrations.Generally, a glass with high dispersion is used for the finished convexcombination spacer lens wafer 485, and an ultraviolet-curable polymer(for example Ormocomp of the ORMOCER® material family from Micro ResistTechnology) with a low dispersion may be used for the top-surfacemounted polymer lens 515. In some cases, however, two different types ofpolymer having different optical dispersions may be used for both thefinished convex combination spacer lens wafer 485 and the top-surfacemounted polymer lens 515.

Referring now to FIG. 14B, finished convex combination spacer lenswafers with top-surface mounted polymer lenses 605 can be stacked toprovide four lenses. While two finished convex combination spacer lenswafers with convex top-surface mounted polymer lenses 605 are shown, oneof the combination spacer lens wafers could be concave, and thetop-surface mounted polymer lenses 515 could be concave. Additionally,any combination of either unfinished 478, 483 (FIGS. 10A, 10B) orfinished combination spacer lens wafers 480, 485 (FIGS. 11A, 11B) can beformed. As such, the number and type of lenses (both top-surface mountedand combination spacer lens wafers) can be tailored to the specificimager's application, while retaining the benefits of simpler assembly,reduced alignment issues, and the prevention of inadvertent tapering ofthrough-holes.

Referring now to FIGS. 12D and 12F, once the finished convex combinationspacer lens wafer 485 (FIG. 11B), or the finished convex combinationspacer lens wafer with top-surface mounted polymer lens 605 (FIG. 13B)is completed, additional processing steps can be performed to improvethe performance of the combination spacer lens wafer. For example, ablack coating 612 may be applied on the inside side-walls enclosing thecombination spacer lens cavity 107 to reduce spurious reflections. Sucha coating would improve the signal-to-noise ratio of the imager module150. Alternatively, an anti-reflective coating 617 may be applied on theinside side-walls and lens enclosing the combination spacer lens cavity107 to reduce spurious reflections and increase the transmission of thelens interface. Another alternative is to form an opaque material (i.e.,black polymer or metal) on top-most portion 497 (FIG. 10B) after it hasundergone any necessary finishing step, and prior to application oftop-surface mounted polymer lenses 515 (FIG. 13B). The opaque materialon top-most portion 497 (FIG. 10B) is formed to have an aperture thatallows light to pass through the lens portion of the combination spacerlens wafer 485 (FIG. 11B).

FIG. 15 shows a block diagram of an imaging device 1100, (e.g. a CMOSimager), that may be used in conjunction with a combination spacer lenswafer 480, 485 (FIGS. 12A, 12B) according to embodiments describedherein. A timing and control circuit 1132 provides timing and controlsignals for enabling the reading out of signals from pixels of the pixelarray 106 in a manner commonly known to those skilled in the art. Thepixel array 106 may use a combination spacer lens wafer, for example480, 485 as shown in FIGS. 12A and 12B. The pixel array 106 of FIG. 15has dimensions of M rows by N columns of pixels, with the size of thepixel array 106 depending on a particular application.

Signals from the imaging device 1100 are typically read out a row at atime using column parallel readout architecture. The timing and controlcircuit 1132 selects a particular row of pixels in the pixel array 106by controlling the operation of a row addressing circuit 1134 and rowdrivers 1140. Signals stored in the selected row of pixels are providedto a readout circuit 1142. The signals are read from each of the columnsof the array sequentially or in parallel using a column addressingcircuit 1144. The pixel signals, which include a pixel reset signal Vrstand image pixel signal Vsig, are provided as outputs of the readoutcircuit 1142, and are typically subtracted in a differential amplifier1160 and the result digitized by an analog to digital converter 1164 toprovide a digital pixel signal. The digital pixel signals represent animage captured by an exemplary pixel array 106 and are processed in animage processing circuit 1168 to provide an output image.

FIG. 16 shows a system 1200 that includes an imaging device 1100 and alens 540 constructed and operated in accordance with the variousembodiments described above. The system 1200 is a system having circuitsthat include imaging device 1100. Without being limiting, such a systemcould include a computer system, camera system, scanner, machine vision,vehicle navigation, video telephone, surveillance system, auto focussystem, star tracker system, motion detection system, imagestabilization system, or other image acquisition system.

System 1200, e.g., a digital still or video camera system, generallycomprises a central processing unit (CPU) 1202, such as a controlcircuit or microprocessor for conducting camera functions thatcommunicates with one or more input/output (I/O) devices 1206 over a bus1204. Imaging device 1100 also communicates with the CPU 1202 over thebus 1204. The processor system 1200 also includes random access memory(RAM) 1210, and can include removable memory 1215, such as flash memory,which also communicates with the CPU 1202 over the bus 1204. The imagingdevice 1100 may be combined with the CPU processor with or withoutmemory storage on a single integrated circuit or on a different chipthan the CPU processor. In a camera system, a lens 540 according tovarious embodiments described herein may be used to focus image lightonto the pixel array 106 of the imaging device 1100 and an image iscaptured when a shutter release button 1222 is pressed. The pixel array106 may have at least one pixel that uses a combination spacer lenswafer 480, 485 as shown in FIGS. 12A and 12B.

While embodiments have been described in detail in connection with theembodiments known at the time, it should be readily understood that theclaimed invention is not limited to the disclosed embodiments. Rather,the embodiments can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed. For example, while some embodiments are described inconnection with a CMOS pixel imaging device, they can be practiced withany other type of imaging device (e.g., CCD, etc.) employing a pixelarray or a camera using film instead of a pixel array.

Although certain advantages have been described above, those skilled inthe art will recognize that there may be many others. For example, thesteps in the methods described herein may be performed in differentorders, or may include some variations, such as alternative materialshaving similar functions. Furthermore, while the specific stacks ofcombination spacer lens wafers are described above in variousembodiments, alternate embodiments including more or fewer lenses arepossible. Accordingly, the claimed invention is not limited by theembodiments described herein but is only limited by the scope of theappended claims.

1. A mold for forming a combination spacer lens wafer, the moldcomprising: a base; a mold feature; and a spacer section connecting thebase to the mold feature.
 2. The mold of claim 1, wherein the moldfeature has a concave portion.
 3. The mold of claim 1, wherein the moldfeature has a convex portion.
 4. The mold of claim 1, wherein theinterface between the spacer section and the base is a first shape, andthe interface between the spacer section and the mold feature is asecond shape.
 5. The mold of claim 4, wherein the first shape and thesecond shape are the same shape.
 6. The mold of claim 1, wherein theinterface between the spacer section and the mold feature is circular.7. The mold of claim 1, wherein the spacer section is tapered.
 8. Themold of claim 7, wherein the cross-sectional area of the spacer sectionto base interface is greater than the cross-sectional area of the spacersection to mold feature interface.
 9. The mold of claim 1, wherein thebase further comprises an alignment element. 10-19. (canceled)
 20. Amethod of forming a combination spacer lens wafer, the methodcomprising: joining a wafer blank with a form mold, the form moldcomprising a base, a mold feature, and a spacer section connecting thebase and the mold feature, such that the base, mold feature, and spacersection are received by the wafer blank; curing the wafer blanksufficiently such that the wafer blank maintains the form of the base,mold feature, and spacer section upon removal of the form mold; andremoving the form mold from the wafer blank.
 21. The method of claim 20further comprising removing a portion of the top-surface material of thecombination spacer lens wafer.
 22. The method of claim 20 furthercomprising heating the wafer blank to facilitate the joining.
 23. Themethod of claim 22, wherein heating the wafer blank occurs before theblank is joined with the form mold.
 24. The method of claim 22, whereinthe wafer blank is cooled after the joining.
 25. The method of claim 20,wherein the form mold is formed to comprise at least one alignmentelement and the wafer blank receives the at least one alignment elementduring the joining.
 26. The method of claim 20, wherein the mold featureis formed to be convex.
 27. The method of claim 20, wherein the moldfeature is formed to be concave.
 28. The method of claim 20 furthercomprising applying a black coating to the sidewalls enclosing acombination spacer lens cavity left by removal of the form mold.
 29. Themethod of claim 20 further comprising applying an anti-reflectivecoating to the side-walls and lens enclosing a combination spacer lenscavity left by removal of the form mold.
 30. The method of claim 20,wherein the wafer blank is an ultraviolet-curable polymer and the curingis conducted by an ultraviolet-radiation source.
 31. The method of claim20, wherein the wafer blank is made of glass.
 32. The method of claim 20further comprising forming a top-surface mounted polymer lens on thecombination spacer lens wafer.
 33. The method of claim 32, wherein thewafer blank is made of glass having a high dispersion and thetop-surface mounted polymer lens is formed from a polymer having a lowdispersion such that chromatic aberrations are minimized.
 34. A methodof forming an imager module, the method comprising: affixing an imagerwafer comprising a die containing a pixel array to a first combinationspacer lens wafer, the first combination spacer lens wafer comprising; acombination lens portion, and a combination spacer portion sized toplace the combination lens portion an appropriate distance from thepixel array, the combination spacer portion being affixed to the die.35. The method of claim 34 wherein the imager wafer comprises aplurality of pixel arrays and the first combination spacer wafercomprises a plurality of combination spacer lenses such that the methodcomprises forming a plurality of imager modules as part of a waferassembly.
 36. The method of claim 34 further comprising covering thesidewalls of the first combination spacer portion that are closest tothe imager array with a black coating.
 37. The method of claim 34further comprising covering the sidewalls of the first combinationspacer portion that are closest to the imager array with ananti-reflective coating, and covering the first combination lens portionclosest to the imager array with an anti-reflective coating.
 38. Themethod of claim 34 further comprising forming the combination lensportion to be convex.
 39. The method of claim 34 further comprisingforming the combination lens portion to be concave.
 40. The method ofclaim 34 further comprising forming a polymer lens mounted on thetop-surface of the first combination spacer lens wafer.
 41. The methodof claim 40 wherein the polymer lens is convex.
 42. The method of claim40 wherein the polymer lens is concave.
 43. The method of claim 34further comprising affixing a second combination spacer lens wafer tothe top-surface of the first combination spacer lens wafer.
 44. Themethod of claim 43 further comprising forming a polymer lens mounted onthe top-surface of the first or second combination spacer lens wafer.